Both the Government and Scottish Executive have announced public consultations on the referendum, including the question's wording. Among the alternatives that could be considered by the Prime Minister are:

Do you want Scotland to remain part of the United Kingdom? This would give the Unionists the advantage of leading the ‘yes’ campaign.

Do you want Scotland to leave the United Kingdom and become an independent country? Unlike Mr Salmond’s version this would explicitly point out that independence means seceding from the UK.

Do you want Scotland to leave the United Kingdom and become a separate nation? The word ‘independence’ has far more positive connotations for voters than ‘separation’ and Mr Salmond loathes the latter term.

Do you think the Scottish Parliament’s powers should be extended to enable independence to be achieved? Mr Salmond insists he already has the power to ask this question and said yesterday he will put it on the ballot paper if Mr Cameron does not allow him to ask his preferred option.

However, Mr Salmond finally admitted he cannot legally ask it without the Government’s permission as constitutional affairs are reserved to Westminster.

This gives the Prime Minister a key bargaining chip when he meets Mr Salmond shortly to discuss transferring the necessary powers for a legal referendum to be conducted.

Prof Cialdini, a professor of Psychology and Marketing at Arizona State University, said the First Minister’s version was loaded as the inclusion of the word ‘agree’ is pejorative and encourages voters to think that is the preferable option.

However, Professor Cialdini, who has conductive extensive research into the elections wording, delivered a damning critique of the First Minister’s preference: He told Radio Four’s Today programme: “I think it’s loaded and biased.

“It sends people down a particular cognitive chute designed to locate ‘agreements’ rather than ‘disagreements’.”

He said it was “correct” that the question contains the presumption that independence is the preferable option, adding; “It’s called a one-sided question or a loaded question and poll-takers for a long time have warned us against those kind of questions.

“When I am asked a question like that, I refuse to answer it because it’s likely to get me to both mistake and misstate my position.”

The professor said there was a “very simple fix to de-biasing” Mr Salmond’s question. Under the First Minister’s proposal, voters would tick either ‘yes’ or ‘no’ to the question of whether they agree with independence.

This would give him the advantage of running the ‘yes’ campaign. However, the professor said it would be fairer to ask two voters separate questions – one whether they agree and one whether they disagree – and asking them to tick one option.

“That produces an even-handed, unbiased approach,” he concluded, adding that the wording of the question can have a “dramatic” effect on the result.

Prof Cialdini cited a study in the US, which asked people a variety of questions about whether people should lower the heating in their homes if there was a fuel shortage.

Depending on how this was posed, he said support for the proposition varied from 38 per cent to only 29 per cent. “A nine per cent swing is enough to change many, many elections,” he said.

His intervention is a damaging blow to the First Minister as the unbiased professor is completely removed from the devolution argument and has never even heard of Mr Salmond.

The First Minister has insisted for weeks that he has the power to stage an “advisory referendum” but yesterday performed an about-turn by admitting that he cannot legally ask his preferred question without the Government’s agreement.

David Cameron has offered to transfer the necessary legal powers, but only if Mr Salmond offers a single, straight question as soon as possible. However, the First Minister yesterday again rejected any “unacceptable conditions” being attached. Lord Forsyth of Drumlean, a former Scotland secretary, accused Scotland First Minister Alex Salmond of proposing a "rigged" referendum and compared him to the leaders of North Korea and Cuba.

He told the House of Lords that if Scotland went ahead with a referendum without consent from Westminster it would have no practical effect and be merely the "most expensive opinion poll in history".

Mr Darling, the Edinburgh South West MP, said: “The question is loaded. He is inviting people to endorse the separation of a successful independent nation. He is not asking if you want to remain part of the United Kingdom, which I would prefer.

“It is asking for trouble and if he tries to push through unfair wording someone will go to court. It’s typical of Salmond who wants to call the shots on the rules, the conduct, the wording and ultimately what the result means.”

Ministers also viewed the wording of the question as unfair and liable to encourage a ‘yes’ vote. One Westminster source said: “This is all about Salmond turning around and saying: ‘Look at all those dreadful people in London trying to tell us what to do.”’

Meanwhile, Danny Alexander, the Chef Secretary to the Treasury, has questioned why Scots will have to wait "a thousand more days" before the vote on independence is held.

Danny Alexander, the Chief Secretary to the Treasury

Mr Alexander questioned the SNP’s plans to hold the vote in the autumn of 2014 and called for “a single clear question on whether or not Scotland should be independent” today.

The Inverness, Nairn, Badenoch and Strathspey MP said: “I remember back in 2009 when the SNP Government last set out plans for a referendum, they said they were going to call it in 2010. So back then they thought they could get the job done in a year.

But John Swinney, the Scottish Finance Minister and former SNP leader, said the autumn of 2014 is the “established date”. He said: “This is the biggest decision in 300 years so it must be founded in a fashion in which people have confidence.

“That means we've got to consult first on the approach to the question, the process, of the referendum. We then have to make sure that Parliament has adequate opportunity to legislate.

“If we were to cut any corners in the legislative process, I'm sure I would be on this programme answering questions about jiggery-pokery.”